1. Field
The invention relates generally to systems and methods for recovering materials from soil and particularly to systems and methods for recovering metals from soil.
2. Description of the Related Art
Solid wastes are generated by many aspects of modern society. Solid wastes from industrial processes, construction/demolition projects and many other human endeavors often contain significant quantities of recoverable materials including soil, rock and gravel aggregates, and metals. Recoverable metals frequently take the form of discrete wastes, waste mixtures, or by-products of the primary process. As such, these materials are sometimes handled, stored, and/or disposed of in a manner that causes them to become mixed with soil or mixed with other solid wastes and particulate debris. Metal bearing soil/particulate debris may be found in stockpiles and in-situ at a wide range of industrial facilities including scrap recycling yards, mills, foundries, landfills, weapons ranges and many abandoned sites previously occupied by similar industries. In some cases, such as landfills and weapons firing ranges, the metal-soil mixture is the result of intentional practices. In most cases, the entire volume of metal bearing soil/debris is rendered unusable for even the most rudimentary reuse, e.g., solid fill disposal, because of its chemical and physical characteristics.
Many jurisdictions enforce environmental regulations that define metal bearing soil/debris as hazardous waste when metal concentrations are elevated. Once the metal bearing soil is classified as hazardous and a “cleanup” is ordered, significant and prohibitive cost and management consequences up to and including comprehensive site remediation are triggered for the waste generator or property owner. The “cleanup” or site remediation practice most commonly employed for metal bearing soil/debris involves a complete excavation of the affected soil volume followed by offsite disposition at an approved facility that is usually remotely located. The financial and logistical impacts of excavation and disposal can be overwhelming for the party responsible for the cleanup and mandatory clean-up orders have led some businesses to financial ruin. In addition to cost, remediation by excavation and disposal incurs its own set of environmental impacts related to increased risk to human health and the environment, and risks associated with transportation such as fuel consumption and the potential release of hazardous materials. Remediation by excavation or disposal ultimately transfers the entire waste volume, including recoverable materials, from one location to another at significant expense and with increased risk to the environment. Another adverse environmental impact associated with remediation by excavation and landfill disposal is the unnecessary consumption of a finite resource; disposal site volume. Disposition of recoverable materials along with the soils not only wastes landfill capacity, it eliminates any opportunity to recover the intrinsic and monetary value of materials that can be reused.
In summary, there is a need for a system and/or processes to treat metal bearing soil/particulate debris to recover the composite portions of recoverable materials from the mixture. Typical portions that can be recovered and separated will include soil, aggregates, metals (ferromagnetic and non-ferrous), and debris. Systems to recover materials from soil will produce economic and environmental benefits by producing a potentially reusable soil component, allowing for recovery of the value of recyclable components, and reducing the volume of affected wastes should landfill disposal of these waste residuals be necessary.